Inkjet printers eject drops of ink through an array of nozzles to effect printing on a media substrate. The nozzles are typically formed on a silicon wafer substrate using semiconductor fabrication techniques. Each nozzle is a MEMS (micro electro-mechanical systems) device driven by associated drive circuitry formed on the same silicon wafer substrate. The MEMS nozzle devices and associated drive circuitry formed on a single nozzle is commonly referred to as a printhead integrated circuit (IC).
Traditional inkjet printers use scanning inkjet printheads. These have a single printhead IC that traverses back and forth across the width of a page as the printer indexes the page along. The Applicant has developed a range of pagewidth printheads that have a nozzle array as long as the printing width of the page. These printheads remain stationary in the printer as the page is fed past. This allows much higher print speeds but is more complicated in terms of controlling the operation of a much larger array of nozzles.
The pagewidth array of nozzles is made up of a series of separate printhead IC's placed end to end. Skilled workers in this field will appreciate that more printhead IC's can be fabricated on the unprocessed circular silicon wafers if each IC is short rather than long. Furthermore, localized fabrication defects can render an entire printhead IC defective. Hence there is less chance that each individual IC will be defective if they are shorter.
The nozzle array is configured into rows and columns with the rows extending the width of the page. The number of rows (that is, the height of the columns) depends on the number of colors (CMY, CMYK or CMYK/IR) and the number of nozzle rows provided for each color plane.
Firing all the nozzles in a row simultaneously draws a large amount of current for a very short period of time. The current steps from zero to a maximum current in a very short time. This creates a high rate of change of current drawn until the maximum value is reached. Unfortunately, a rapid increase in the current creates inductance and so increases the circuit impedance. With high impedance, the drive voltage ‘sags’ until the inductance returns to normal, i.e. the current stops increasing. In printhead IC's, it is necessary to keep the actuator supply voltage within a narrow range to maintain consistent ink drop size and directionality.